What an ADU shell build covers

A shell build takes a detached ADU from raw dirt to a finished, weathertight structure with all the hard structural and mechanical work complete. The stopping point is finished white drywall, with windows and doors installed and all rough-ins ready for final trades. Here's what we handle on a shell build:

Site prep and foundation

• Demo and site clearing (as needed)

• Grading and drainage

• Utility trenching from the main house to the ADU

• Foundation excavation, rebar, forms, and concrete pour, handled in-house through our sister company Supreme Concrete Group

Structural construction

• Framing

• Roofing

• Exterior siding and finishes

• Windows and exterior doors installed

Mechanical rough-ins

• Electrical rough-in (wires pulled, boxes set, panel installed)

• Plumbing rough-in (supply and drain lines in place)

• HVAC rough-in (ductwork and equipment set, if included in your plans)

Interior shell

• Insulation

• Drywall hung, taped, and finished to a paint-ready state (no paint, no texture)

Permitting and inspections through the shell stage

• Coordinating plan submittal with the city or county

• Managing inspections through the shell phases

• Passing all inspections up to the point where interior finish work begins

What's not included:

• Paint, flooring, cabinets, countertops, trim, and interior doors

• Plumbing and electrical fixtures (toilets, sinks, faucets, light fixtures, outlets, switches)

• Appliances

• Final inspection and certificate of occupancy (which requires the interior finishes to be complete)

If you want us to handle everything through final walkthrough, see our Detached ADU Builds service instead. If you want to handle the shell yourself and bring us in for specific phases, see our Owner-Builder Support page. For the full menu of options, see all our ADU services.

Who a shell build fits best

A shell build is the right fit if:

• You want to save on labor by doing the interior finishes yourself. Finishes are the phase where DIY savings are biggest because it's where the most labor-hours go.

• You're comfortable handling (or subbing out) flooring, paint, trim, cabinets, and fixtures. These are lower-risk trades than structural work, and many homeowners tackle them with good results.

• You have the time to finish the interior on your own timeline. Shell builds work well for owners who aren't in a rush to move in and can pace the finish work over several months.

• You want the expensive, high-skill, high-risk parts done right by professionals. Foundation, framing, roofing, and mechanical rough-ins aren't where you want to cut corners. A shell build lets you hire out exactly those phases.

A shell build probably isn't the right fit if:

• You want to be in the ADU as fast as possible. Shell + self-finish is usually slower than a full build handled by one contractor.

• You don't have time or interest in managing subs or doing the finish work yourself. A shell build trades labor cost for your time and attention on the interior phase.

• You're planning to rent the ADU out quickly. Rental timelines usually favor full builds so the unit is income-ready sooner.

Shell build vs. full turnkey build

The main trade-off between a shell build and a full build is cost vs. time and effort.

A shell build costs less up front because you're paying a contractor for structural and mechanical work only, then handling interior finishes yourself (or hiring finish trades directly). You save on labor for the finish phase, but the project takes longer overall and you're managing the finish work yourself.

A full detached ADU build costs more because you're paying one contractor to take the project from dirt to move-in ready. You save time, stress, and coordination effort, and the ADU is finished faster and usually ready for occupancy or rental sooner.

Neither is objectively better. It depends on your budget, your timeline, and how much of the project you want to personally manage.

If you're in between (you want help with specific phases but not the whole project) our Owner-Builder Support service might be a better match.

What sets TrueBuild apart on shell builds

Foundations poured in-house
The foundation is the most expensive and most critical phase of a shell build, and it's where most shell build quotes vary the most. We pour every foundation in-house through our sister company Supreme Concrete Group. Same owner, same crew, same quality control. See our Concrete ADU Foundations page for more on how that works.

Honest scope definition
Some builders quote "shell" and mean different things: some stop at framing, some include drywall, some include windows, some don't. We define the stopping point clearly before we bid, in writing, so you know exactly what you're getting and exactly what you're taking on yourself. No shell-build gray area.

Jose on every project
Shell builds still need owner attention. The coordination between structural, framing, and rough-in trades is where shell builds go sideways if nobody's paying attention. Jose runs every shell project personally, same as every full build.

A clean handoff
When we finish a shell build, we leave you with a permit-ready, inspection-passed structure and clear documentation of what's complete and what's left. You shouldn't have to guess what the next trade needs to start their work.

What to expect on timeline

Shell builds move through the first part of a full ADU build, then stop. A typical detached ADU shell build timeline:

1. Pre-construction (plans and permits): 2–6 months. Same as a full build, because permits don't care whether you're finishing the interior or not.

2. Shell construction: 3–4 months. Slightly shorter than a full build because the finish phase is skipped.

3. Shell inspections and handoff: 1–2 weeks.

Your total project timeline depends heavily on how fast you handle the interior finishes yourself after the shell is done. Some owners take 2–3 months, others take a year or more. That's your call.

What affects ADU shell build cost

Shell build pricing depends on the same factors as a full build, minus the finish phase: size, site complexity, utility connections, and your jurisdiction's permit fees.

Shell builds typically run somewhere in the range of 65–80% of a full build cost, depending on the specific shell scope. That's a meaningful savings, but it assumes you handle the finishes yourself or hire finish trades directly. If you hire a general contractor to finish the interior after the shell is done, you'll usually pay more in total than if one builder did the whole job.

We don't publish fixed per-square-foot pricing because it misleads more than it informs. For an honest bid on your specific shell project, schedule a free consultation.

Common questions about ADU shell builds

What exactly is a "shell build"?
A shell build is a detached ADU finished to the point of being weathertight and structurally complete, with all mechanical rough-ins done and interior drywall hung and finished, but without paint, flooring, cabinets, fixtures, or appliances. The owner handles those final finishes themselves or hires finish trades directly.

Do you do weathertight-only shells (no drywall)?
Sometimes, depending on the project. Weathertight-only (framed, roofed, sided, windows and doors installed, but no rough-ins or drywall) is a narrower scope. It's less common because homeowners usually want the mechanical rough-ins done professionally. We can quote either scope if you're clear on what you want.

Can I do some of the shell work myself and have you do the rest?
Yes, that's closer to our Owner-Builder Support service. We can take on specific phases (foundation, framing, mechanical rough-ins) without doing the full shell. Works best when you've thought through which phases you're comfortable handling and which you want a pro for.

Do shell builds pass city inspections?
Shell builds pass the structural, framing, rough-in, and insulation/drywall inspections, which are the inspections that happen during the shell phase. Final inspection and certificate of occupancy require the interior finishes to be complete, which is on you after the shell handoff.

Will my shell ADU be livable as-is?
No. A completed shell isn't a habitable dwelling. It doesn't have plumbing or electrical fixtures, no flooring, no cabinets or kitchen fixtures, and hasn't passed final inspection. It's a structure ready for you to finish, not a move-in-ready home.